1. Field of the Invention
This invention relates to illumination devices and systems, and in particular, it relates to illumination devices and systems useful in stage lighting.
2. Description of the Related Art
LED (light emitting diodes) light sources are clean and energy efficient light sources. The achievable luminous flux of LED light sources increases every year. Currently, LED light sources are mostly used in low power, low end color-changing lighting products.
Most high power stage lights currently use metal halide discharge lamps. Such lamps are white light sources, and have relatively short life, typically from a few hundred to a few thousand hours. As the emission spectrum of metal halide discharge lamps is a continuous white spectrum, color lights of various colors required by stage lighting are obtained by using color filters. Such color lights and the resulting projected patterns have relatively low color saturation, and their colors are neither very vivid nor very rich. To increase the saturation of monochromatic light obtained by such a system, color filters with very narrow transmission bands may be used, but this decreases the brightness of the monochromatic light.
Using LED light sources for stage lighting can achieve monochromatic lights without using filters. Further, by adjusting the drive current of LEDs of various base colors (e.g. primary colors), desired colors of the output monochromatic light can be achieved. By taking advantage of the relatively high saturation of monochromatic LED light sources, a great number of colors can be achieved for stage lighting, making the system more flexible. However, current LED light sources tend to generate a large amount of heat, and their light emitting efficiency is still relatively low. As single LED chips still cannot provide sufficiently high output power, high power stage lighting systems must rely on LED arrays to achieve the desired luminous flux.
Chinese patent application No. 200720061982.0 describes a light source system for stage lighting, which employs a LED array and a large heat dissipation device to provide a power of 100 W. This system can also achieve adjustable color by controlling the power of the LEDs of different colors within the system. However, due to concerns on heat dissipation and luminous flux, as well as uniformity of brightness and color of the output light, this system still cannot satisfy the need for high power stage lighting systems.
To overcome the problems of the above system, an improved system is described in a Chinese patent application filed by the applicant of this application. This system employs a wavelength-based light combining device to combine monochromatic lights from multiple LED arrays into one light beam. This system offers increased output power and improved uniformity of brightness and color of the output light.
Current stage lighting systems that employ LED array, such as those described above, have certain shortcomings, in particular: When such systems are used to generate a white light, the light generating efficiency is lower than the efficiency of traditional metal halide discharge lamps. One reason is that metal halide discharge lamps are hot light sources, so their light output efficiency is virtually unaffected by heat generation, i.e., regardless of the output power of the light source, their light generating efficiencies are substantially unchanged. For example, a currently available 575 W stage lamp outputs 49000 lumens of light, at an efficiency of about 85 lumens/W; a 1200 W stage lamp outputs 110000 lumens of light, again at an efficiency of about 85 lumens/W. By contrast, in high power LED light sources which combine monochromatic lights to generate white light, the following factors cause a decrease in white light generating efficiency at high power: On the one hand, green LED chips (i.e. LED chips that emit green light) currently have relatively low electrical to light conversion efficiency, blue LEDs have relatively high efficiency, and red LEDs have an efficiency in between; on the other hand, a white spectrum has the most green component, less red component, and the least blue component. This means that to adjust the white balance, when combining the three colored LED lights, the output power of the blue and red lights have to be lowered, resulting in a low overall efficiency.